Dr. Monica Elliott Ft. Lauderdale REC BASIC PLANT PATHOLOGY Dr. Monica Elliott Ft. Lauderdale REC

WHAT IS A HEALTHY PLANT? You can’t diagnose a plant problem without knowing how the plant looks when healthy!

Ask the right questions! PLANTS DON’T TALK! Information about a plant sample must come from person managing the plant ! Ask the right questions!

Abiotic vs. Biotic

But, first rule out those pesky insects

Sooty mold is a fungus, but not a pathogen Sooty mold is a fungus, but not a pathogen. It is feeding off insect excretions, such as honeydew.

Abiotic Biotic Injuries Pathogen is the problem Disorders Pathogen is not causing problem Biotic Pathogen is the problem

A destructive physical occurrence to the plant INJURY A destructive physical occurrence to the plant

INJURY Lightning strikes, Tire tracks Car or lawn equipment exhaust NO pathogen! Lightning strikes, Tire tracks Car or lawn equipment exhaust Animals - moles, armadillos, urine

DISORDER Interaction between the plant & its environment that is usually associated with imbalances of physical or chemical require- ments for plant growth.

DISORDERS Nutritional, usually deficiencies Air pollution NO pathogen! Cold or heat stress Nutritional, usually deficiencies Air pollution Excessive rainfall or drought Pesticide phytotoxicity

Cold Damage

Both too much and too little water can cause disease-like symptoms. Drought Oedema Both too much and too little water can cause disease-like symptoms.

Sunburned palm leaf

Manganese deficiency

Manganese deficiency

Potassium deficiency

SPOTS & PATCHES A plant with a spot does not automatically mean it has a disease. A yellow or dead patch in the lawn does not mean there is a disease.

Chinchbug damage

Typical injury from growth regulator type herbicide

DISEASE Interaction between the plant and a pathogen that disrupts the normal growth and appearance of the plant.

DISEASE Susceptible host Virulent pathogen Conducive environment Three Components: Susceptible host Virulent pathogen Conducive environment Disease Triangle

Types of Pathogens Bacteria Phytoplasmas (mlo) Viruses Viroids Fungi large small

Most bacteria can be cultured on artificial media. Phytoplasmas, viruses and viroids cannot be cultured on media.

Most fungi can be cultured on artificial media, but not all.

PATHOLOGY TERMS that is body of fungus. MYCELIA: thread-like material that is body of fungus. SPORES: reproductive structures of a fungus or bacterium

Bacteria – most enter through natural openings or wounds Viruses – transmitted through wounds made mechanically or by vectors Phytoplasmas – transmitted by vectors Fungi – enter through natural openings, wounds; or by mechanical pressure or enzymes they produce

FUNGUS - FUNGI No chlorophyll, so no self energy PATHOGEN: obtains energy from living things SAPROPHYTE: obtains energy from dead things SAME fungus can be BOTH a pathogen and a saprophyte!

PATHOLOGY TERMS the fact it has a disease SYMPTOMS: how plant expresses the fact it has a disease leaf spots, patches, tip die back, etc. SIGNS: actual pathogen parts associated with a diseased plant spores, mycelia, conks, mushrooms

Signs of Disease

Signs of Disease

Signs of Disease

Plant Organs And Functions Disease Symptoms

Symptoms spot – small, distinct lesion on leaf, fruit . . . blight – spots that have coalesced or merged together; more tissue being affected rot – tissue is breaking down (fruit, roots); usually mushy, but can be dry wilt – plant droops due to water stress; can be systemic (xylem) or due to root rot

Symptoms gall – masses of undifferentiated growth; usually on stems or woody tissue (branches) but can be on roots - wart, clubroot, witches’-broom canker – sunken lesions; usually on stems or woody tissue patches, decline – terms often used in association with grasses (turf, grain crops)

Symptoms Caused by Bacteria leaf spots and blights – water soaked, greasy soft rots of fruits wilts (systemic – xylem) gall (overgrowths/cell proliferation) cankers

Symptom: Water soaked or greasy leaf spots

Symptom: Water soaked or greasy leaf blight

Symptom: Wilt Symptom: Gall

Symptoms Caused by Viruses dwarfing or stunting to some degree mosaics – light green, yellow or white areas intermingled with green – leaves or fruits ring spots – chlorotic or necrotic rings – leaves, fruits or stems are always systemic infections

Symptom: Dwarfing and Stunting

Symptom: Mosaic

Symptom: Ringspot

Symptoms Caused by Fungi leaf spots and blights (including rust and powdery mildew) soft or dry rots of fruits, bulbs . . . root rots wilts (systemic – xylem) overgrowths/cell proliferation – clubroot, galls, warts, witches’-broom scabs, cankers, patches and decline

Symptom: Leaf spots and blight

Symptom: Soft or dry rots

Symptom: Wilt

Symptom: Patches and Decline

PATHOLOGY TERMS does or does not cause a disease yes or no question PATHOGENESIS: the pathogen either does or does not cause a disease yes or no question VIRULENCE: severity level of the disease that a pathogen causes minimal damage vs. dead plant

Plant Samples Goal is to have plant sample arrive in diagnostic laboratory looking like it did in the field or landscape. Keep roots moist, but do not place any other tissue inside plastic bag. Ask the right questions, fill out form completely. It is critical to have background information about the situation.

Plant Samples Ask the right questions: What is the plant? Where is plant growing? Is this sample typical? When did symptoms appear? Fertility and pesticide applications?

Plant Samples

Plant Samples Best samples are those that exhibit progression of symptoms – e.g., leaf spot to leaf blight to severely diseased plant. Best to examine entire plant, if possible, as root disease could be cause for leaf symptoms Good pictures are useful, illustrating overall symptoms and close-ups

Plant Samples Soil samples for disease diagnosis are useless. Do not be afraid to tell a client that the sample is inadequate. We are not miracle workers! It is better to make no diagnosis than to make the wrong diagnosis, especially if it is a valuable specimen or pesticides are required.

Three “Little” Steps 2. Identify the conditions 1. Identify the disease. 2. Identify the conditions causing disease diagnosed. 3. Identify the management techniques that will alter the disease-conducive conditions causing disease diagnosed. SureLook Holmes

DISEASE Susceptible host Virulent pathogen Conducive environment Three Components: Susceptible host Virulent pathogen Conducive environment Disease Triangle

Plant Disease Control Integrated Approach Pathogen exclusion or sanitation Plant resistance (genetic) Cultural methods Chemical methods

Plant Disease Control Pathogen exclusion - via regulation - via ‘just don’t bring it home no matter how cute it looks’ if it has a spot, wilt, etc.

Plant resistance (genetic) Plant Disease Control Plant resistance (genetic) Immunity is the rule in the plant kingdom Where immunity does not exist, plant breeders have developed cultivars with resistance to specific pathogens.

Plant Disease Control Plant resistance (genetic)

Plant Disease Control Plant resistance (genetic) - breeding for resistance to pathogen - plant adaptation to site (right plant for the right site concept) - monoculture vs. mixed culture

Plant Disease Control Cultural methods - crop rotation - host eradication (alternate hosts) - improved plant environment, especially water management

Plant Disease Control Cultural methods - sanitation of tools, pots, shoes, equipment, etc.

Plant Disease Control Chemical methods - seed treatments - soil treatments/root drenches - foliar sprays - trunk injections

Plant Disease Control Chemical methods critical to understand that chemicals do not necessarily eliminate symptoms observed most chemicals prevent disease from ever occurring or keep it from spreading

Plant Disease Control Chemical methods ex: leaf spots don’t disappear, but old leaves with spots die and new growth is healthy and spot free ex: rotted roots eventually die, but new roots are healthy and take their place to supply water and nutrients

Plant Disease Control Chemical methods “The label is the law.” Pesticide labels must be followed, even by homeowners – safety to applicator and environment. The site for application must be on the label – turf vs. ornamentals.

Some diseases do not have ANY control methods. Plant Disease Control Some diseases do not have ANY control methods.

Proactive vs. Reactive The single best method for controlling diseases is to prevent them!